The present invention relates to a discharge of a back-up capacitor by constant current.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
In the case of a high-voltage battery, a backup capacitor which can take up short-term power spikes is generally arranged downstream of the high-voltage battery. In normal mode, the high-voltage battery is connected to utility arrangements via a main switch, such that they are supplied with electrical energy via the high-voltage battery. In the event of a fault, the high-voltage battery is disconnected from the utility arrangements. To ensure voltage tolerance and contact safety, the back-up capacitor has to be discharged as well. The discharge is realized by energizing the discharge path so that the electrical energy stored in the back-up capacitor is converted into thermal energy.
In the art, the back-up capacitor is discharged by connecting the back-up capacitor directly to a discharge resistor. The discharge operation takes place in a relatively short space of time (a few seconds). The current characteristic follows an exponentially falling curve. After the back-up capacitor has been discharged, it is necessary to wait a relatively long time (approx. 1 min) before connecting the high-voltage battery again. Otherwise, when the high-voltage battery has to be disconnected from the utility arrangements again, the resistor would be thermally overloaded. The resistor must be designed both for maximum voltage (usually several 100 V) and for high power spikes. Additionally, it is difficult to dissipate heat generated in the discharge resistor, since connection of the discharge resistor to heat sinks and a housing is permitted only via an electrical insulation.
It would therefore be desirable and advantageous to address these and other prior art shortcomings.